How the Brain Awakens from Unconsciousness Becomes Clearer

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Exactly what happens when people wake up from anesthesia or a
coma has long baffled scientists, but now new research on rats
suggests the path the brain takes to regain consciousness may be
even more sophisticated than thought.

"It is commonly assumed that waking from anesthesia is
a simple thing: The drugs leave the brain, and the effects they
produced in the brain get washed out, and the brain somehow
recovers," said Dr. Alex Proekt, an assistant professor of
anesthesiology at Weill Cornell Medical College in New York. "But
that 'somehow' part is poorly understood."

The researchers looked at the brain's activity patterns,
hypothesizing that the activity follows a structured path,
changing in a specific way as the brain moves toward
consciousness. The researchers wanted to know whether the brain
moves from one activity state to the next, in a stepwise fashion,
or whether the brain can go from any given state to a number of
other states, and therefore, that there are multiple routes to
consciousness.

To examine the brain's trajectory while recovering consciousness,
Proekt and colleagues recorded the electrical activity of certain
brain regions in anesthetized rats. They slowly lowered the
concentration of anesthetic vapor that the animals were
breathing, until they eventually woke up.

The analysis of the rats' brain activity suggested that the brain
passes through several distinct activity states to become
conscious. The researchers found that only certain transitions
between activity states are possible, and some states do form
hubs that connect groups of otherwise disconnected states.
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"Although many paths through the network are possible, to
ultimately enter the activity state compatible with
consciousness, the brain must first pass through these hubs in an
orderly fashion," the researchers wrote in their study published
today (June 9) in the Proceedings of the National Academy of
Sciences.

The researchers said the new findings could one day be used to
help people in a coma. The brains of people under anesthesia as
well as comatose patients show an electrical pattern known as
burst suppression, which is characterized by periods of spikes in
activity, alternating with periods of silence.

Both
general anesthesia and coma are major perturbations to
brain's normal activity, and in some cases, the brain cannot find
its way back to consciousness.

"Some people, after injury, will remain in some minimally
conscious state forever, but some people can recover years after
the injury," Proekt said.

"One interesting possibility is that perhaps the injury can act
to remove some of these loops, so in a sense you are trapped in
one of these states," Proekt told Live Science.

In order to help comatose patients, scientists will first have to
examine whether the same phenomenon they observed in rats also
exists in the human brain, and then explore how it may be
possible to push the brain out of one state so it can proceed
further toward recovery, Proekt said.

Awake during surgery

Although anesthesiologists have long been able to successfully
put people to sleep, they still can't be 100 percent sure that a
patient is
truly unconscious, rather than just unable to respond.

Understanding the transitions between activity states that happen
during the brain's recovering from anesthesia may be the first
step to finding a way to detect when someone is on the verge of
waking up, Proekt said.

"It's not a common problem, but it is a petrifying scenario to
imagine -- being paralyzed and awake for surgery," he said.

Studies have suggested that a very small number of patients
experience awaking during surgery, but it is also possible that a
larger number of people have some awareness during surgery but
don't recall afterwards, Proekt said.